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| Prion (bird) |
Prion (bird):For the infectious agent bearing the same name, see prion.
Fairy Prion, P. turtur
Slender-billed Prion, P. belcheri
Fulmar Prion, P. crassirostris
Broad-billed Prion, P. vittata
Antarctic Prion, P. v. desolata
Salvin's Prion, P. v. salvin
A prion is a petrel (genus Pachyptila) found in Antarctica and nearby islands. Prions grow 20–27 cm long, and have blue-grey plumage with white underparts. The flattened bill has a fringe of strainers. Prions feed on small invertebrates from the sea.
The Antarctic Prion and the Salvin's Prion are usually considered to be races of the Broad-billed Prion.
External links
- [http://news.bbc.co.uk/2/hi/science/nature/3961069.stm Antarctic Prion homes on their life mate through smell]
Category:Procellariiformes
Prion:This article is about the infectious particles known as prions. For the bird, see Prion (bird).
Prions — short for proteinaceous infectious particle — are infectious protein structures that replicate through conversion of other host proteins. Though the exact mechanisms of their actions and reproduction are unknown, it is now commonly accepted that prions are responsible for a number of previously known but little-understood diseases generally classified under transmissible spongiform encephalopathy diseases (TSEs), including scrapie (a disease of sheep), kuru (found in members of the cannibalistic Foré tribe in Papua New Guinea), Creutzfeldt-Jakob disease (CJD), Chronic Wasting Disease, Fatal Familial Insomnia (FFI), Gerstmann-Sträussler-Scheinker syndrome (GSS), and bovine spongiform encephalopathy (BSE or mad cow disease) (Collinge, 2001). These diseases affect the structure of brain tissue and all are fatal and untreatable.
Prion hypothesis
The theory that TSEs are caused by an infectious agent made solely of protein has been around since the 1960s (Alper, 1967; Griffith, 1967). However, it was not until 1982 that the prion protein itself was discovered, by Stanley B. Prusiner of UCSF, who was awarded the Nobel Prize in physiology or medicine in 1997 for this discovery (Prusiner, 1982). Prusiner coined the word "prion" by combining the first two syllables of the words "proteinaceous" and "infectious". It should be noted that Prusiner intended the word 'prion' to be pronounced [http://www.webster.com/cgi-bin/audio.pl?prion001.wav=prion 'pree-on'].
Prior to Prusiner's insight, all known pathogens (bacteria, viruses, etc.) contained nucleic acids that are necessary for reproduction. The prion hypothesis was developed to explain the discovery that the mysterious infectious agent causing Creutzfeldt-Jakob disease resisted ultraviolet radiation (which breaks down nucleic acids), yet responded to agents that disrupt proteins (Alper, 1967). Initially, this hypothesis was highly controversial, because it seemed to contradict the "central dogma of modern biology", which asserts that all living organisms use nucleic acids to reproduce. The "protein-only hypothesis" — that a protein (which, unlike DNA, has no obvious means of replication) could reproduce itself — was initially met with skepticism. However, evidence has steadily accumulated in support of this hypothesis, and it is now widely accepted. Rather than contradicting the central role of DNA, however, the prion hypothesis suggests a special case in which merely changing the shape, or conformation, of a protein (without changing its amino acid sequence) can alter its biological properties. The actual synthesis of the prion protein is still carried out by the ribosome, while the infectious form of the prion protein only transfers the pathological conformation to the proteins synthesized by the cell.
A breakthrough occurred when researchers discovered that the infectious agent consisted mainly of a specific protein, which Prusiner called PrP, an abbreviation for "prion-related protein". This protein is found in the membranes of normal cells (its precise function is not known), but an altered shape distinguished the infectious agent. The normal one is called PrPC, while the infectious one is called PrPSc (the 'C' refers to 'cellular' PrP, while the 'Sc' refers to 'scrapie', a prion disease occurring in sheep) (Oesch, 1985). It is hypothesized that the distorted protein somehow induces normal PrP structure to also become distorted, producing a chain reaction that both propagates the disease and generates new infectious material. Since the original hypothesis was proposed, a gene for the PrP protein has been isolated (the Prnp gene) (Oesch, 1985), several mutations that cause the variant shape have been identified and successfully cloned, and studies using genetically altered mice have bolstered the prion hypothesis.
Although the identity and general properties of prions are now well-understood, the mechanism of prion infection and replication remains mysterious. It is generally assumed that PrPSc directly interacts with PrPC to cause the normal form of the protein to rearrange its structure. One idea, the "Protein X" hypothesis, is that an as-yet unidentified cellular protein (Protein X) enables the conversion of PrPC to PrPSc by bringing a molecule of each of the two together into a complex (Telling, 1995).
The degenerative diseases caused by prions are known collectively as "transmissible spongiform encephalopathies" or TSEs (Collinge, 2001).
Useful prions in yeast and other fungi
Not all prions are dangerous; in fact, prion-like proteins are found naturally in many (perhaps all) plants and animals. Because of this, scientists reasoned that such proteins could give some sort of evolutionary advantage to their host. This was suggested to be the case in a species of fungus Podospora anserina. Genetically compatible colonies of this fungus can merge together and share cellular contents such as nutrients and cytoplasm. A natural system of protective "incompatibility" proteins exists to prevent promiscuous sharing between unrelated colonies. One such protein, called HET-S, adopts a prion-like form in order to function properly (Coustou, 1997). The prion form of HET-S spreads rapidly throughout the cellular network of a colony and can convert the non-prion form of the protein to a prion state after compatible colonies have merged (Maddelein, 2002). However, when an incompatible colony tries to merge with a prion-containing colony, the prion causes the "invader" cells to die, ensuring that only related colonies obtain the benefit of sharing resources .
In 1965, Brian Cox, a geneticist working with the yeast Saccharomyces cerevisiae, described a genetic trait (termed [PSI+]) with an unusual pattern of inheritance. Despite many years of effort, Cox could not identify a conventional mutation that was responsible for the [PSI+] trait. In 1994, yeast geneticist Reed Wickner correctly hypothesized that [PSI+] as well as another mysterious heritable trait, [URE3], resulted from prion forms of certain normal cellular proteins (Wickner, 1994). It was soon noticed that heat shock proteins (which help other proteins fold properly) were intimately tied to the inheritance and transmission of [PSI+] and many other yeast prions. Since then, researchers have unravelled how the proteins that code for [PSI+] and [URE3] can convert between prion and non-prion forms, as well as the consequences of having intracellular prions. When exposed to certain adverse conditions, [PSI+] cells actually fare better than their prion-free siblings (True, 2000); this finding suggests that, in some proteins, the ability to adopt a prion form may result from positive evolutionary selection (Harrison, 2002). It has been speculated that the ability to convert between prion infected and prion-free forms enables yeast to quickly and reversibly adapt in variable environments. Nevertheless, Wickner maintains that [URE3] and [PSI+] are diseases [http://www.pnas.org/cgi/content/abstract/102/30/10575].
As of 2003, the following proteins in Saccharomyces cerevisiae had been identified or postulated as prions:
- Sup35p, forming the [PSI+] element;
- Ure2p, forming the [URE3] element;
- Rnq1p, forming the [RNQ+] element (also known as [PIN+]);
- New1p, forming the [NU+] element.
Prions have also been speculatively linked to memory [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=14697205] and cellular differentiation, the process by which stem cells take on specialized functions (such as muscle or blood cells).
Molecular properties of prions
A great deal of our knowledge of how prions work at a molecular level comes from detailed biochemical analysis of yeast prion proteins.
blood
A typical yeast prion protein contains a region (protein domain) with many repeats of the amino acids glutamine (Q) and asparagine (N); these Q/N-rich domains form the core of the prion's structure. Ordinarily, prion domains are flexible and lack a defined structure. When they convert to the prion state, several molecules of a particular protein come together to form a highly structured amyloid fiber (see figure at left). The end of the fiber acts as a template for the free protein molecules, causing the fiber to grow. Small differences in the amino acid sequence of prion-forming regions lead to distinct structural features on the surface of prion fibers. As a result, only free protein molecules that are identical in amino acid sequence to the prion protein can be recruited into the growing fiber. This "specificity" phenomenon may explain why transmission of prion diseases from one species to another (such as from sheep to cows or from cows to humans) is a rare event.
humans
The mammalian prion proteins do not resemble the prion proteins of yeast in their amino acid sequence. Nonetheless, the basic structural features (formation of amyloid fibers and a highly specific barrier to transmission between species) are shared between mammalian and yeast prions. The prion variant responsible for mad cow disease has the remarkable ability to bypass the species barrier to transmission.
The figure at right shows a model of two conformations of PrP; on the left is the known, normal, alpha helical PrPC structure (to explore/download see the [http://www.rcsb.org/pdb/cgi/explore.cgi?pid=257211117306887&page=0&pdbId=1AG2 RSCB Protein Databank]), while on the right is a proposed model of how the abnormal PrPSc form might look. Although the exact 3D structure of PrPSc is not known, there is increased β sheet content (green arrows) in the prion version of the molecule (Pan, 1993). These β sheets can lead to amyloid aggregation.
Classification
See also
- nanobacterium
References
- Alper T, Cramp WA, Haig DA, Clarke MC (1967). Does the agent of scrapie replicate without nucleic acid? Nature 214 (90), 764-766
- Collinge J (2001). Prion diseases of humans and animals: their causes and molecular basis. Ann. Rev. Neurosci. 24, 519-550 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11283320&query_hl=7]
- Coustou, V et al (1997). The protein product of the het-s heterokaryon incompatibility gene of the fungus Podospora anserina behaves as a prion analog. Proc. Natl. Acad. Sci. USA 94 (18), 9773-78 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=9275200&query_hl=9]
- Griffith JS (1967). Self-replication and scrapie. Nature 215, 1043-1044
- Harrison P et al (2002). A small reservoir of disabled ORFs in the yeast genome and its implications for the dynamics of proteome evolution. J. Mol. Biol. 316 (3), 409-419 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11866506&query_hl=13]
- Maddelein, ML et al (2002). Amyloid aggregates of the HET-S prionprotein are infectious. Proc. Natl. Acad. Sci. USA 99 (11), 7402-7 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12032295&query_hl=15]
- Oesch B, et al (1985). A cellular gene encodes PrP 27-30 protein. Cell 40 (4), 735-746 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=2859120&query_hl=17]
- Pan, KM et al (1993). Conversion of alpha-helices into beta-sheets features in the formation of scrapie prion protein. Proc. Natl. Acad. Sci. USA 90 (23), 10962-66 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7902575&query_hl=19]
- Prusiner SB (1982). Novel proteinaceous infectious particles cause scrapie. Science 216 (4542), 136-144 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=6801762&query_hl=21]
- Telling GC, et al (1995). Prion propagation in mice expressing human and chimeric PrP transgenes implicates the interaction of cellular PrP with another protein. Cell 83 (1), 79-90 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7553876&query_hl=24]
- True HL, et al (2000). A yeast prion provides a mechanism for genetic variation and phenotypic diversity. Nature 407 (6803), 477-483. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11028992&query_hl=5]
- Wickner, RB (1994). [URE3] as an altered URE2 protein: evidence for a prion analog in Saccharomyces cerevisiae. Science 264 (5158), 566-569. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7909170&query_hl=26]
External links
- [http://www.mad-cow-facts.com Mad Cow Disease] Information from the Center for Global Food Issues.
- [http://www.madcowering.com Madcowering] A BSE-TSE blog.
- [http://www-micro.msb.le.ac.uk/3035/prions.html Prion Diseases] (2003). Dr. Sean Heaphy, Leicester University.
- [http://www.sciencemag.org/feature/data/prusiner/245.shl Prion Diseases and the BSE Crisis] (1997). Article from Science magazine by Stanley Prusiner, discoverer of prions.
- [http://www.sciam.com/article.cfm?articleID=0009FD80-C3C6-1C5A-B882809EC588ED9F The Prion Diseases] (1995). Article from Scientific American magazine by Stanley Prusiner.
Category:Biochemistry
Category:Genetics
-
Category:Proteins
ja:プリオン
ko:프리온
Petrel:This article is about the petrel seabirds.
The petrels are seabirds in the bird order Procellariiformes. They occur in four families within that group, which also includes the Albatross family, Diomedeidae. Having a fossil record that extends back at least 60 million years, it is among the older bird groupings, other than the ratites, with distant ties to penguins and loons. However, recent research shows that the Galliformes (Pheasants, Grouse and relatives), and Anseriformes (ducks, geese and swans) are older.
All the members of the order are exclusively pelagic in distribution — returning to land only to breed.
The family Procellariidae is the main radiation of medium-sized 'true petrels', characterised by united nostrils with medium septum, and a long outer functional primary. It is dominant in the Southern Oceans, but not so in the Northern Hemisphere.
It includes a number of petrel groups
- The fulmars: 7 species: surface predators and filter feeders, breed in high latitudes but migrate along cool currents to he north. All but Fulmarus essentially confined to the south, Fulmarus apparently colonised the N hemisphere during the Tertiary.
- The huge giant petrels, genus Macronectes, which are convergent with the albatrosses.
- The true fulmars, genus Fulmarus
- Antarctic Petrel Thalassoica antarctica
- Cape Petrel Daption capense
- Snowy Petrel Pagodroma nivea.
- The prions, genus Pachyptila. A specialised group of six very numerous species, all southern. They have a small, fulmar-like form and filter-feed on zooplankton.
- The gadfly petrels. These are large and agile short-billed petrels in the genus Pterodroma which include the endangered Bermuda Petrel (or Cahow).
- Shearwaters - the genera Calonectris and Puffinus
- Procellaria petrels
- Petrels of indeterminate relationships
- Bulwer's Petrel Bulweria bulwerii and Jouanin's Petrel Bulweria fallax
- Blue Petrel Halobaena caerula
- Kerguelen Petrel Lugensa brevirostris
- Tahiti Petrel Pseudobulweria rostrata.
The family Hydrobatidae is the storm-petrels, small pelagic petrels with a fluttering flight which often follow ships.
The family Pelacanoididae is the four species of diving petrels, genus Pelacanoides. These are auk-like small petrels of the southern oceans.
The taxonomy of the petrels is complex, and several genera are intermediate.
Etymology
The word "petrel" comes from the Latin name for the Christian Saint Peter, and refers to the habits of certain species to hover just above the ocean waves, with their feet barely touching the water, thus giving an appearance of walking on water, as St. Peter is said to have done.
Category:Procellariiformes
Category:Seabirds
Antarctica
:For the Kim Stanley Robinson novel, see Antarctica (novel)
Antarctica (from Greek ἀνταρκτικός, "opposite the Arctic") is a continent surrounding the Earth's South Pole. It is the coldest place on Earth and is almost entirely covered by ice; however, it is also the world's largest desert.
Although myths and speculation about a Terra Australis ("Southern Land") go back to antiquity, the first commonly accepted sighting of the continent occurred in 1820 and the first verified landing in 1821 by the Russian expedition of Mikhail Lazarev and Fabian Gottlieb von Bellingshausen. (See also History of Antarctica.)
With an area of 13,200,000 km², Antarctica is the fifth largest continent, after Asia, Africa, North America, and South America. However, it is by far the smallest in population: indeed, it has no permanent population at all. It is also the continent with the highest average altitude, and the lowest average humidity of any continent on Earth, as well as the lowest average temperature.
It has been assigned the Internet ccTLD .aq.
Antarctic climate
.aq
Antarctica is the coldest place on earth. Temperatures reach a minimum of between -85 and -90 degrees Celsius in the winter and about 30 degrees higher in the summer months. Weather fronts rarely penetrate far into the continent, leaving the center cold and dry. There is little precipitation over the central portion of the continent, but ice there can last for extended time periods. However, heavy snowfalls are not uncommon on the costal portion of the continent, where snowfalls of up to 48 inches in 48 hours have been recorded. Nearly all of Antarctica is covered by an ice sheet that is, on average, 2.5 kilometers thick.
At the edge of the continent, strong katabatic winds off the polar plateau often blow at storm force. In the interior, however, windspeeds are often moderate.
Depending on the latitude, long periods of constant darkness, or constant sunlight, mean that climates familiar to humans are not generally available on the continent.
Geography
katabatic wind
The continent of Antarctica is located mostly south of the Antarctic Circle, surrounded by the Southern Ocean. Physically Antarctica is divided in two by mountains close to the neck between the Ross Sea and the Weddell Sea. The portion of the continent west of the Weddell Sea and east of the Ross Sea is called Western Antarctica and the remainder Eastern Antarctica, since they correspond roughly to the eastern and western hemispheres relative to the Greenwich meridian. Western Antarctica is covered by the West Antarctic Ice Sheet.
See also: Extreme points of Antarctica, Antarctic territories.
Population
It is usually estimated that at a given time there are at least 1,000 people living in Antarctica. This varies considerably with season.
Generally, stations use their home country's time zone, but not always; where known, a base's UTC offset is listed. Although Antarctica has no permanent residents, a number of governments maintain permanent research stations throughout the continent. Many of the stations are staffed around the year. These include:
staffed
- Akademik Vernadsky Station, Galindez Island, (), ( UKR)
- Amundsen-Scott South Pole Station, South Pole United States Antarctic Program
- Belgrano II, () Laboratory and meteorological station Argentine southernmost base (since 1979).
- Bellingshausen Station, King George Island ()
- Bernardo O'Higgins Station, Antarctic Peninsula, Chilean Army.
- Casey, Vincennes Bay ( Australian Antarctic Division) (UTC+8)
- Comandante Ferraz Station, King George Island ()
- Concordia Research Station, (75° S 123° E),
- Dakshin Gangotri Station, Indian Antarctic Program
- Davis, Princess Elizabeth Land ( Australian Antarctic Division) (UTC+7)
- Dumont d'Urville Station () (UTC+10)
- Eduardo Frei Montalva Station and Villa Las Estrellas, King George Island, Chilean Air Force.
- Esperanza () Laboratory and meteorological station (since 1952). Radio LRA Arcángel, School #38 Julio A. Roca (since 1978), tourist facilities.
- General Artigas Station ()
- Georg von Neumayer Station, () (Atka-Bay) (Alfred Wegener Institute )
- Great Wall Station (), King George Island ()
- Halley Research Station () British Antarctic Survey
- Henryk Arctowski Polish Antarctic Station (), King George Island
- Jubany, (), since 1953 ()
- King Sejong Station (), King George Island, since 1988 ()
- Machu Picchu Research Station, Admiralty Bay, King George Island, summer base established in 1989.
- Macquarie Island ( Australian Antarctic Division)
- Maitri Station, () near Schirmacher Region ( Indian Antarctic Program)
- Marambio Base, () Seymour-Marambio Island. Laboratory, meteorological station, 1.2 km long, 30 m wide landing track (since 1969) () [http://www.marambio.aq website]
- Mawson Station, Mac Robertson Land ( Australian Antarctic Division) (UTC+6)
- McMurdo Station, Ross Island () (UTC+12, follows New Zealand DST)
- Mirny Station () ()
- Mizuho Station () (National Institute of Polar Research )
- Molodezhnaya Station () ()
- Novolazarevskaya Station, Dronning Maud Land () ()
- Orcadas () Orcadas Islands (since 1904)()
- Palmer Station, Anvers Island () (UTC-4, follows Chilean DST)
- Professor Julio Escudero base, King George Island.
- Progress Station () ()
- Rothera Research Station () British Antarctic Survey (UTC-3)
- San Martín Station () (since 1951) Laboratory and Meteorological measurements ()
- SANAE (South African National Antarctic Expeditions), on the Fimbul Coastal Ice Shelf in Queen Maud Land
- Saint Climent Ohridski () (since 1988) Biology Research, Laboratory and Meteorological measurements. First Orthodox Church - St. Ivan Rilski ()
- Scott Base, () Ross Island () (UTC+12, follows New Zealand DST)
- Showa Station () (National Institute of Polar Research ) (GMT+3)
- Troll Station (Norwegian Polar Institute), () Queen Maud Land ()
- Vostok, Antarctica () () (UTC+6)
- Zhongshan (Sun Yet-Sen) Station () ()
Emilio Marcos Palma was the first person born in Antarctica (Base Esperanza) in 1978, his parents being sent there along with seven other families.
Emilio Marcos Palma
Communications
The international dialing code for Antarctica is +672.
Antarctica has wireless telephone services. There is a single cell tower using AMPS technology at Argentina's Marambio Base and an Entel Chile GSM tower on King George Island. Communications are otherwise limited to satellite connections.
Radio frequencies that can be used are FM2 and shortwave 1.
Military
The Antarctic Treaty prohibits any measures of a military nature in Antarctica, such as the establishment of military bases and fortifications, the carrying out of military maneuvers, or the testing of any type of weapon. It permits the use of military personnel or equipment for scientific research or for any other peaceful purposes.
The United States military issues the Antarctica Service Medal to those members of the military or civilians who perform research duty on the Antarctica continent. The medal, including the winter-over bar issued to those who remain on the continent for two complete, six-month seasons, is properly awarded by the United States Congress.
The only documented large-scale land military maneuver was "Operación 90," undertaken 10 years before the Antarctic Treaty by the Argentinian military.
See also
- South Pole
- Southern Ocean
- Antarctic Treaty System
- Climate of Antarctica
- Communications in Antarctica
- Demographics of Antarctica
- Ecology of Antarctica
- Economy of Antarctica
- Flags of Antarctica
- History of Antarctica
- Antarctica territories
- List of antarctic and sub-antarctic islands
- Transportation in Antarctica
- Mount Erebus disaster
- Antarctic Stamps
- Diamond dust, an Antarctic optical phenomenon
- Life in the Freezer, a BBC television series on life on and around Antarctica
- Extreme points of Antarctica
- Wildlife of Antarctica - Krill, Penguins, Pinniped (Seals, Sea Lions, Fur seal), Whales
- Ice, Iceberg, Ice shelf, Glacier
External links
- [http://www.70south.com 70South]
- [http://www.ats.org.ar Antarctic Treaty Secretariat]
- [http://www.anetstation.com ANetStation]
- [http://www.add.scar.org The Antarctic Digital Database - a source of digital topographic map data for Antarctica]
- [http://www.ejercito.mil.ar/antartico/historia/antarti_hist.htm Argentine Antarctic history]
- [http://www.aad.gov.au/ Australian Antarctic Division]
- [http://www.antarctica.ac.uk British Antarctic Survey]
- [http://www.comnap.aq/ Council of Managers of National Antarctic Programs (COMNAP)], official homepage.
- [http://www.awi-bremerhaven.de/Polar/index.html German Antarctic Ships and Stations]
- [http://www.loc.gov/rr/international/frd/antarctica/antarctica.html Portals on the World - Antarctica] from the Library of Congress
- [http://www.polarmuseum.sp.ru/Eng/ The Russian State Museum of Arctic and Antarctic]
- [http://www.scar.org The Scientific Committee for Antarctic Research - coordinating body for Antarctic Science]
- [http://members.eunet.at/castaway/stations/aa-bases.html Antarctic Research Stations]
- [http://www.cia.gov/cia/publications/factbook/geos/ay.html The World Factbook – Antarctica] from the U.S. Central Intelligence Agency
- [http://www.70south.com Latest Antarctic news and information by 70South]
- [http://www.planetavivo.org/english/ResearchPrograms/Antarctica/SlideShows/ArdleyIsland/ArdleyIsland1.html Biodiversity at Ardley Island, South Shetland archipelago, Antarctica]
- [http://www.iaato.org International Association of Antarctic Tour Operators (IAATO)]
Category:Continents
Category:Antarctica
Category:Special territories
Category:Lists of coordinates
ja:南極大陸
ko:남극
ms:Antartika
simple:Antarctica
th:ทวีปแอนตาร์กติกา
zh-min-nan:Lâm-ke̍k-tāi-lio̍k
Plumage
----
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds. They are the outstanding characteristic that distinguishes the Class Aves from all other living groups. Other Theropoda also had feathers (see Feathered dinosaurs).
Characteristics
Feathers are among the most complex structural organs found in vertebrates: integumentary appendages, formed by controlled proliferation of cells in the epidermis, or outer skin layer, that produce keratin proteins. The β-keratins in feathers, beaks and claws — and the claws, scales and shells of reptiles — are composed of protein strands hydrogen-bonded into β-pleated sheats, which are then further twisted and crosslinked by disulfide bridges into structures even tougher than the α-keratins of mammalian hair, horns and hooves.
Feathers insulate birds from water and cold temperatures. Individual feathers in the wings and tail play important roles in controlling flight. These have their own identity and are not just randomly distributed. Although feathers are light, a bird's plumage weighs two or three times more than its skeleton, since many bones are hollow and contain air sacks. Colour patterns serve as camouflage against predators for birds in their habitats, and by predators looking for a meal. As with fish, the top and bottom colors may be different to provide camouflage during flight. Striking differences in feather patterns and colours are part of the sexual dimorphism of many bird species and are particularly important in selection of mating pairs. The remarkable colors and feather sizes of some species have never been fully explained.
There are two basic types of feather: vaned feathers which cover the exterior of the body, and down feathers which are underneath the vaned feathers. The pennaceous feathers are vaned feathers. Also called contour feathers, pennaceous feathers are distributed over the whole body. Some of them are modified into remiges, the flight feathers of the wing, and rectrices, the flight feathers of the tail. A typical vaned feather features a main shaft, called the rachis. Fused to the rachis are a series of branches, or barbs; the barbs themselves are also branched and form the barbules. These barbules have minute hooks called barbicels for cross-attachment. Down feathers are fluffy because they lack barbicels, so the barbules float free of each other, allowing the down to trap much air and provide excellent thermal insulation. At the base of the feather, the rachis expands to form the hollow tubular calamus, or quill, which inserts into a follicle in the skin.
skin
A bird's feathers are replaced periodically during its life through molting, new feathers are formed through the same follicle from which the old ones were fledged.
Some birds have a supply of powder-down feathers which grow continuously, with small particles regularly breaking off from the ends of the barbules. These particles produce a powder that sifts through the feathers on the bird's body and acts as a waterproofing agent and a feather conditioner. Most waterbirds produce a large amount of powder down. Waterproofing can be lost by exposure to emulsifying agents due to human pollution. Feathers can become waterlogged and birds may sink. It is also very difficult to clean and rescue birds whose feathers have been fouled by oil spills.
Bristles are stiff, tapering feathers with a large rachis but few barbs. Rictal bristles are bristles found around the eyes and bill. They serve a similar purpose to eyelashes and vibrissae in mammals.
Origins
Feathers most likely originated as a filamentous insulation structure, or possibly as markers for mating, with flight emerging only as a secondary purpose. It had been thought that feathers evolved from the scales of reptiles, but recent research casts doubt on this homology (see Quarterly Review of Biology 77:3 (September 2002): 261-95). Experiments show that the same protein (when missing before birth) that causes bird feet to stay webbed, causes reptile scales to become feathers. [http://www.dinosauria.com/jdp/archie/scutes.htm]
Feathered dinosaurs
Main article: Feathered dinosaurs
Although birds use feathers primarily for flight, several dinosaurs have been discovered with feathers on their limbs that would not have functioned for flight. One theory is that feathers originally developed on dinosaurs as a means of insulation; those small dinosaurs that then grew longer feathers may have found them helpful in gliding, which would have begun the evolutionary process that resulted in some proto-birds like Archaeopteryx and Microraptor zhaoianus. Other dinosaurs discovered with feathers include Pedopenna daohugouensis, Sinosauropteryx, and Dilong paradoxus. Currently the question is whether birds are deinonychosaurians or dromaeosaurids, not whether birds are dinosaurs. It has been suggested that Pedopenna is older than Archaeopteryx, however, their age remains doubted by some experts. Dilong is a tyrannosauroid which predates Tyrannosaurus rex by 60 to 70 million years.
Human uses
Feathers are both soft and excellent at trapping heat; thus, they are sometimes used in high-class bedding, especially pillows, blankets, and mattresses. They are also used as filling for winter clothing, such as quilted coats and sleeping bags; goose down especially has great loft, the ability to expand from a compressed, stored state to trap large amounts of compartmentalized, insulating air. Bird feathers have long been used for fletching arrows and in the past were used for ink pens. They have also been put to use as sexual aids; see feather dancing. Colorful feathers such as those belonging to pheasants have been used in the past to decorate hats and fishing lures. Eagle feathers have great cultural value to American Indians. Various birds and their plumages serve as cultural icons throughout the world, from the hawk in ancient Egypt to the bald eagle and the turkey in the United States. In Greek mythology, Icarus tried to escape his prison by attaching feathered wings to his shoulders with wax, which melted near the Sun.
References
Category:Animal products
ja:羽根
InvertebrateInvertebrate is a term coined by Jean-Baptiste Lamarck to describe any animal without a spinal column. It therefore includes all animals except vertebrates (fish, reptiles, amphibians, birds and mammals).
Lamarck divided these animals into two groups, the Insecta and the Vermes, but nowadays, they are classified into over 30 phyla, from simple organisms such as sponges and flatworms to complex animals such as arthropods and mollusks.
Since invertebrates include all animals except a certain group, invertebrates form a paraphyletic group, but, despite not forming a "natural group" (that is, monophyletic), "invertebrate" is still a widely used term. It is not uncommon for books entitled "Invertebrate Zoology" to be found. This reflects the bias in society and also in zoology towards larger, more complex animals that are more closely related to humans. Thus, there are relatively many scientists studying (and relatively much funding available for the study of) birds, mammals, reptiles, and so on, but far fewer scientists studying invertebrates, even though invertebrates include 97% of all animal species.
For a full list of animals considered to be invertebrates, see animal. All the listed phyla are invertebrates along with two of the three subphyla in Phylum Chordata: Urochordata and Cephalochordata. These two, plus all the other known invertebrates, have only one cluster of Hox genes, while the vertebrates have duplicated their original cluster more than once.
External links
- [http://reference.allrefer.com/encyclopedia/categories/invertz.html Invertebrate Zoology]
- [http://digitalcommons.unl.edu/onlinedictinvertzoology/ Online Dictionary of Invertebrate Zoology]
- [http://www.goliathus.cz/en/museum-homepage-0.html Online museum] of many invertebrates, provided by [http://www.goliathus.cz/ goliathus.cz].
Category:Animals
ms:Invertebrata
ja:無脊椎動物
Gheorghe TatarescuGheorghe Tătărescu (1886, Targu-Jiu - 28 March 1957, Bucharest) was a Romanian politician that was two times Prime Minister of Romania.
Terms as Prime Minister
- 3 January 1934 - 28 December 1937
- 25 November 1939 - 4 July 1940
Tatarescu, Gheorghe
Tatarescu, Gheorghe
Tatarescu, Gheorghe
Tatarescu, Gheorghe
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